Nature is undoubtedly the best teacher for mankind, and human beings have been inspired by the physiological characteristics of animals and plants to invent equipment, which can be widely used in daily life, medical treatment and military equipment, such as Luban saws, live nematode drug delivery and bionic chameleon military camouflage.
Recently, scientists inspired by the swing of the tail of the Asian lizard tiger, developed two bionic lizard tiger flexible robots, which are expected to play a key role in the smooth and safe landing of flying robots such as drones.
Picture | Asian Lizard Tiger Soft Robot Simulation (Source: Communications Biology)
The paper was published Sept. 2 in Communications Biology under the title "The tail makes the sliding gecko head down and hit the trunk for a stable landing," by Ardian, a professor at the Max Planck Institute for Intelligent Systems In research in Germany Jusufi) serves as corresponding author.
Figure | related papers (Source: Communications Biology)
So far, in the dynamic flight of birds, bats and many insects, the landing force may be much lower than the take-off force, and the reduction of pre-landing speed is mainly achieved by the wings. For wingless animals such as squirrels, lizards and frogs, landing is subjected to huge ground gliding forces, and they turn to the landing target at a relatively high speed.
In contrast, the Asian Lizard Tiger studied by the team has very high wing loads compared to most gliders. By recording gliding trajectories, the team's researchers found that the Asian Lizard Tiger's gliding horn was about twice as steep as that of special gliders such as lizards, and that gliding was half that of other animals.
Different species have their own unique ways of landing from the air to the vertical ground. The team mainly conducted quantitative analysis of lizard tigers living in southeast Asian rainforests, recorded the trajectory of Asian lizard tigers when gliding at high speeds, and found that Asian lizard tigers did not slow down before making contact with the trunk, but prevented falling by adjusting the head impact, body contact angle and tail swing behavior.
Figure | trajectory of an Asian lizard tiger jumping from an elevated platform to a branch (Credit: Communications Biology)
The team used a group experiment to further explore whether the steady landing of asian lizard tigers is closely related to the "swing of the tail". The researchers took 30 samples of Asian lizard tigers, observed their jumps from a location in the forest to trees, and then recorded the downward jump trajectory of 16 of them with a more accurate camera.
The landing process of the Asian lizard tiger can be divided into five stages. First, when the Asian lizard tiger jumps to the target position, its body needs to tilt upwards by only 16 ± 8.4°. When this movement is completed and falls from the air, the head and front of the torso of the Asian lizard tiger begin to contact and undergo kinetic energy transfer, and the collision of the head and torso increases the angular momentum, causing the torso to move under the trunk.
Next, the hind legs of the Asian lizard tiger touch the surface of the vertical branches, and instead of sliding from the tree to the forest floor, it arched its hind legs in the direction of the ventral side. In the fourth stage, the forefoot begins to detach from the branches beyond the attached branches. In the final stage, the Asian lizard tiger presses its tail against the tree and leans back, and the body part begins to rotate backwards away from the focus point.
The first impact of the head on a branch will give the Asian lizard tiger a large pitch angle kinetic energy, it can generate a long arm force through the swing of the tail, so that the tiger's body by leaning backwards to gradually hedge this power, and finally successfully land with less force. The team refers to this particular action as the "Fall Arrest Response" (FAR).
As a result, the team found three situations, most of the Asian lizard tigers can land steadily on the branches, a small number of Asian lizard tigers because they do not control the balance is slipped to the ground, especially the tailless Asian lizard tigers, even if they can stay for a short time, but finally failed to land on the branches smoothly.
Figure | the trajectory of the Asian lizard tiger landing on a branch (Source: Communications Biology)
Therefore, scientists boldly imagined whether the Asian lizard tiger could jump down from a high place and land smoothly, and the "swing of the tail" was the core factor that prevented it from falling. So the scientists developed two soft-bodied robots similar to the Asian Lizard Tiger Institution to further validate this idea.
Picture | Asian Lizard Tiger Soft Robot Simulation Experiment (Source: Communications Biology)
The head of the Asian Lizard Tiger Soft Body Robot can first collide with ballistic short-range dive at a landing speed of 6.0 ± 0.9 m/s. The posture changes constantly during landing, gradually tilting upwards as you approach the point of focus, remaining constant at 53 ± 5.8°. Through the speed map of the gliding duration, when they can be seen approaching the target of the branches, the Asian lizard gecko reduces its speed and tries to stabilize the landing.
Figure | landing pitch behavior of a robot with a tail (Source: Communications Biology)
Due to the lack of specialized aerodynamic forms, 4 out of 21 geckos were still accelerating at the time of impact. As a result, Asian lizard tigers reduce their speed by 60% before landing, avoiding increasing the risk of injury or falling to the forest floor when landing at high speeds.
Successful and failed landings can be observed in experiments with lizard soft robots, where failed landings characterized in dynamic models are not controlled by pitch, and hind feet are lost in contact with the point of focus. Pitch allows the Lizard Tiger soft robot model to consume more slowly and less angular momentum gained in the initial stages of landing, so the gradual and complete deceleration and absorption of gliding kinetic energy is more likely than no pitch and partial detachment from the landing surface.
The team's experimental demonstration of the physical model of the lizard soft robot proves that the stability of the landing can be enhanced through mechanical mediation, and it is expected that the flying robots such as drones will land stably and safely on the vertical ground in the future.